This invention relates to articles molded from resinous plastic material which incorporate a flexible, resilient covering layer thereover, especially of leather. The invention also relates to methods for manufacturing such articles including injecting moldable resinous plastic material behind a leather or other covering layer such that the molded layer is securely bonded to the covering layer. A particular aspect of the present invention is directed to a cover for an occupant restraint air bag in a vehicle having an outer layer of leather or another flexible resilient covering material, and a method for manufacturing such covers, especially where the cover includes a frangible tear seam in a desired pattern adapted to separate upon inflation of an air bag to release the air bag into the vehicle when the cover is installed thereover.
The advent of supplemental occupant restraint systems for vehicles, better known as air bags, has required covers within the vehicle interior to house the air bag until needed. These covers must properly release the air bag into position in the vehicle when inflated upon sudden deceleration of the vehicle. Use of such covers has required efforts to properly match the covers to the vehicle interior decor and trim materials. In many vehicles, leather is used to cover portions of the instrument panel, seats, door panels, and steering wheel and post and it is desirable to incorporate leather on air bag covers incorporated in such vehicles. However, difficulties have arisen in attempting to use leather on air bag covers.
First, natural leather is a nonuniform material whose thickness, tear strength and surface finish vary over a wide range. Attempts have been made to glue or otherwise adhere pieces of leather over molded or other preformed air bag covers. However, release of the air bags using such covers has been unsatisfactory because the strength of the covering leather often prevents proper opening of the cover to release the bag. Difficulties have also arisen in obtaining proper adhesion of the leather to the preformed cover. The leather will loosen and/or peel away from the underlying part over time. Other attempts have incorporated leather sheets sewn or otherwise made from multiple leather pieces. However, such products have required raised, sewn seams and have not provided the desired smooth finished leather look desired by vehicle manufacturers. Moreover, the labor intensive costs associated with producing such covers have been high, and it has often been difficult to properly align the seams in such fabricated leather sheets with a desired separation pattern for the air bag cover. This also restricts proper release of the air bag.
A concurrent problem in the use of leather covered, molded articles generally has been the inability to obtain a proper leather grain appearance on the exposed surface of the article. Manufacturing procedures in applying leather covers to preformed articles with adhesives and the like have often diminished the naturally appearing grain in the leather and provided an almost smooth appearance instead of the desired natural leather grain. In addition, it has been difficult with past procedures to properly adhere the leather to a preformed article such that the leather remains secured to the article for proper appearance over its life.
Yet another problem encountered with covers for vehicle air bags has been the difficulty in obtaining proper air bag release over the wide range of temperatures in which the typical vehicle is expected to operate. In many air bag covers, a separation line of reduced strength has been provided such that the cover will separate into flaps which bend back to provide an opening through which the bag is released. However, in subzero temperatures, when the covers are made from various resinous plastic materials, the tensile strength of the plastic is greatly reduced due to the brittleness of the plastic at such low temperatures. Thus, prior known molded plastic air bag covers have often fractured prematurely in extremely low temperatures, or have failed to properly release the air bag upon inflation in such temperatures.
The present invention was conceived to overcome these and other problems encountered with leather covered molded plastic articles, and especially molded plastic air bag covers for vehicle restraint systems incorporating a leather or other flexible, resilient outer layer.